Dedupe

- Fixed regression in Exists predicate

- Fixed regression in Exists predicate

- Development in python packaging made supporting the previous namespace approach for
variable plugins untenable. Since we had to redo the way we defined the data model,
we took the opportunity to explicity instantiate variable objects.

- fixed bug that was preventing learning of index predicates in Dedupe mode

- Improved memory performance of connected components

- Python 3 only
- Static typing and type Hints
- Incorporate sqlite to extend normal API to millions of records
- Multiprocessing enabled for Windows
- Multiprocessing mode changed to spawn for Mac OS X
- Moved from CamelCase to lowercase_with_underscore for method names.
- Dropped ability to save indices in save settings.
- Moved from Deduper.match -> Dedupe.partition, RecordLink.match -> RecordLink.join, Gazetteer.match -> Gazetteer.search
- Renamed Matching.blocker -> Matching.fingerprinter
- Moved to autodoc for documentation
- Dropped threshold methods
- matchBlocks has been replaced by score, which takes pairs of records not blocks